LibTorch C++ frontend on Android

Mobile
1

I am developing a C++ library with LibTorch and want to use its C++ frontend on Android.

I’ve successfully linked LibTorch to the library by unpacking the official AAR release, but it seems like I cannot use torch/torch.h from it. I found this header in headers/torch/csrc/api/include/torch/torch.h but if I include this directory to use #include <torch/torch.h> in my code I get this error:

In file included from <my project>\app\src\main\cpp\Test.cpp:6:
In file included from <my project>\app\.cxx\Debug\x311e382\x86_64\_deps\torch-src\headers\torch\csrc\api\include\torch\torch.h:3:
In file included from <my project>\app\.cxx\Debug\x311e382\x86_64\_deps\torch-src\headers\torch\csrc\api\include\torch\all.h:13:
In file included from <my project>\app\.cxx\Debug\x311e382\x86_64\_deps\torch-src\headers\torch\csrc\api\include\torch\nn.h:4:
In file included from <my project>\app\.cxx\Debug\x311e382\x86_64\_deps\torch-src\headers\torch\csrc\api\include\torch\nn\functional.h:11:
In file included from <my project>\app\.cxx\Debug\x311e382\x86_64\_deps\torch-src\headers\torch\csrc\api\include\torch\nn\functional\normalization.h:4:
<my project>\app\.cxx\Debug\x311e382\x86_64\_deps\torch-src\headers\torch\csrc\api\include\torch\nn\functional\padding.h:4:10: fatal error: 'ATen/native/PadNd.h' file not found

The Making Native Android Application that uses PyTorch prebuilt libraries article doesn’t explicitly include headers/torch/csrc/api/include directory, so does this mean that PyTorch’s C++ frontend is unavailable on Android?

2

Hi Tim, I had the same problem and was able to solve it as I described here: https://discuss.pytorch.org/t/cmake-error-during-pytorch-mobile-custom-build/112843/9?u=scheckmedia. After that I was able to compile everything as expected.

3

Wow, thanks, just adding PadNd.h from <PyTorch sources dir>/aten/src/ATen/native to <unpacked PyTorch AAR dir>/headers/ATen/native makes the project build and run.

But since I’m just using the prebuild binaries, won’t something break if I actually call something that uses the contents of PadNd.cpp? I mean, is this source file included into the prebuild .so files for Android?

4

That’s a good question I have no answer for. I’ve compiled libtorch with the changes I made manually and never observed any issues but I think too, using the prebuild binaries and the applied changes might produce issues.

5

I found this issue about the exact same problem and seems like it hasn’t been fixed yet. Asked there if copying PadNd.h like this will cause any trouble later.

6

As one of the devs replied in the issue, copying PadNd.h shouldn’t break anything.

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